A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface.
When a read/write head is being positioned (or “loaded”) onto the magnetic-recording disk to perform a read or write operation, the head “descends” off the mechanical landing ramp to its flying height. Similarly, when a read/write head is moved off (or “unloaded”) the disk, the head “ascends” from its flying height to land on the mechanical landing ramp. However, when the read/write head ascends or descends, the mechanical movement often makes the instant flying height fluctuate and causes the read/write head to make physically “contact” with the surface of the magnetic-recording disk. Such contact is prone to occur when a read/write head performs loading/unloading sequences. Any contact is undesirable as it increases the likelihood of physical damage of the read/write head, and thus, decreases the reliability and the lifetime of the hard drive.
The read/write head of a HDD is mounted on a head slider and secured to a flexure that is flexibly mounted to an electrical lead suspension. The angle (or orientation) of the head slider is termed “attitude.” Whenever the head slider is not flying over the surface of the magnetic-recording disk, the head slider is deemed to be in a free state. A measure of attitude of the head slider under this free state is termed “static attitude.” The static attitude can be measured with reference to the pitch and roll axes of the suspension. Therefore, a pitch static attitude (PSA) and a roll static attitude (RSA) may be obtained by measuring the pitch and roll axes of the read/write head respectively. In an ideal situation, the value of both PSA and RSA should be zero degrees, meaning that the head slider is positioned perfectly when not flying. However, due to variation in the manufacturing process, mounting, and other factors, each HDD manufactured invariably has slightly different PSA and RSA parameters. Any non-zero static attitude is called a “static attitude deviation,” as it deviates from the ideal number—zero. Non-zero PSA and RSA results in the read/write head being positioned in a less than optimal position and in more frequent and heavier contacts during loading/unloading sequences.